Consuming the Earth: the biophysics of sustainability

By William Rees

William Rees is Director of UBC's School of Community and Regional Planning and winner of a 1996 UBC Killam Prize. The following article is the premise of his remarks at the American Association for the Advancement of Science held last month in Seattle.

The underlying premise of this paper is that much of economics is, or should be, human ecology. The economy is that set of activities and relationships by which human beings acquire, process, and distribute the material necessities and wants of life. It therefore includes that subset of activities by which humankind interacts with the rest of the ecosphere. If we were dealing with any other species, these relationships would indisputably fall within the realm of "ecology." To this extent then, economists are arguably human ecologists.

One thing that both economists and ecologists agree upon is that human beings are consumer organisms. In fact, in today's increasingly market-based society people are as likely to be called "consumers" as they are citizens, even when the context is a non-economic one. The designated role of people in the economy is to consume the goods and services produced by businesses, which are the other major component of the economy.

Ecologists would actually refer to humans as macro-consumers. In general, macro-consumers depend on other organisms, either green plants or other animals, which they consume directly to satisfy their metabolic needs. However, a complete human ecology would also have to consider the consumption demands of our manufactured capital. Indeed, the major ecological difference between humans and other species is that in addition to our biological metabolism, the human enterprise is characterized by an industrial metabolism. All our toys and tools, factories and infrastructure, are the external equivalent of organs and, like bodily organs, require continuous flows of energy and material from and to the environment for their production, maintenance, and operation.

Economists and ecologists also both see humans as producers. We can only marvel at the enormous quantity of goods and services, both essential and frivolous, that advanced economies have spewed into a willing marketplace. However, there is a fundamental difference between production in nature and production in the economy. In nature, green plants are the factories. Using the simplest of low-grade inorganic chemicals (mainly water, carbon dioxide and a few mineral nutrients) and an extra-terrestrial source of relatively low-grade energy--light from the sun--plants assemble the high-grade fats, carbohydrates, proteins, and nucleic acids upon which most other life forms and the functioning of the ecosphere are dependent. Because they are essentially self-feeding and use only dispersed (high entropy) substances for their growth and maintenance, green plants are called primary producers.

By contrast, human beings and their economies are strictly secondary producers. The production and maintenance of our bodies and all the products of human factories require enormous inputs of high-grade energy and material resources from the rest of the ecosphere. That is, all production by the human enterprise, from the increase in population to the accumulation of manufactured capital, requires the consumption of a vastly larger quantity of available energy and material first produced by nature. This last point is critical when we consider that people and their economies are part of nature. Indeed, humans have become the major consumer organism in virtually all the significant ecosystems types on earth--in structural terms, the expanding human enterprise is positioned to consume the ecosphere from within.

Since the beginning of the industrial revolution, human populations have been growing, material standards have been rising, and increasingly sophisticated methods have been developed for resource extraction and "harvesting." Ever greater quantities of energy and material are used for the manufacture and maintenance of productive capital and for the production of goods and services. On this basis, one might argue a priori that the rate of resource consumption by industrial economies will inevitably come to exceed the rate of production by local ecosystems. In the absence of trade, such economies are fundamentally unsustainable. The global economy is, of course, the aggregate of all the national ones, but in the aggregate can trade with no one. It's not much of a stretch, therefore, to suggest that the present global economy is also fundamentally unsustainable.